A better understanding of how the liver regenerates in response to toxic injuries, such as from drug exposure or viral infection, will lead to new treatments with an immense impact on liver disease. We have developed an innovative genetic screen to identify and rank - for the first time - key regulators of liver repopulation following toxic injury. We have discovered two exceptional associations among the >40 genes: (1) Foxa3, a transcription factor that is known to be important for liver development, is one of the strongest promoters of liver repopulation, and (2) Tumor Necrosis Factor Receptor 1 (TNFR1), important for signaling of inflammation in hepatocytes and previously thought to help initiate liver regeneration, was found to be the most significant suppressor of repopulation among all the genes tested. The hypothesis of this proposal is that Foxa3 and TNFR1 play critical roles in regulating liver regeneration. We propose the following Specific Aims: Specific Aim 1: To investigate the mechanisms underlying Foxa3-mediated promotion of liver repopulation. Specific Aim 2: To assess whether TNFR1 deletion and targeted anti-TNF therapy can promote liver repopulation. The experimental approach outlined here is designed to carefully dissect the roles of Foxa3 and TNFR1 in regulating liver regeneration, and to assess the clinical significance of these findings. We will identify how genetic deletion of Foxa3 and TNFR1 affects liver repopulation. We will characterize the protein domains and the genomic DNA binding sites of Foxa3 that are necessary to enhance repopulation. Finally, we will assess the signaling pathway for TNFR1 that inhibits repopulation and whether drugs targeting TNFR1 inflammatory signaling can improve liver repopulation. This proposal also outlines my 5-year plan to continue to develop as a physician-scientist in Gastroenterology, with the goal of becoming an independent principle investigator. As a clinician, I plan to focus in hepatology, and with a sub-focus on adults with congenital disorders of the liver. As a scientist, I will continue to flourish under th mentorship of Dr. Kaestner, and will continue to engage with the lab in regular meetings and journal clubs. I will meet semi-annually with an advisory committee consisting of senior physician-scientists in gastroenterology, Drs. Ben Stanger and Michael Pack. I plan to submit manuscripts to high-impact journals and to obtain funding from the NIH and from GI societies. The Gastroenterology Division at the University of Pennsylvania has a long track record of preparing successful physician-scientists and is an ideal environment for my maturation toward independent laboratory investigation.